The present invention relates to a display driver which drives an image display device such as a Liquid Crystal Display, and more particularly, to a technique effectively applied to a drive circuit and a driving method of an active-matrix display device which is capable of partial display.
For example, active-matrix display devices are used for mobile devices such as mobile phones and handheld terminals, due to them having characteristics of being thin, light, and having low power consumption. For mobile devices, generally the power supply consists of batteries and so improvements in lowering power consumption are required. However, in recent years, while the progress of higher resolution displays due to demands with respect to improvements in viewability and image quality has increased, the power consumption of these devices has also increased. To solve this problem, it is known that a partial display technique is effective, which achieves low power consumption by displaying only a minimum required part in the display during standby or in a power-saving mode.
Further, for LCDs, to prevent burn-in which leads to image deterioration, reversed-polarity voltages corresponding to image data at a constant frequency must be applied to the liquid crystals. Therefore, even for still images, it is necessary to execute image data transfer from a system of a previous stage such as a microprocessor (MPU: Micro Processing Unit) which increases power consumption and the load on the MPU. To solve this problem, liquid crystal drivers are made to store image data by embedding memories to store image data of one screen image. Accordingly, it is possible to apply reversed-polarity voltages to liquid crystals in a constant frequency using the stored image data while displaying a still image. Reducing transfers of the MPU to reduce power and load thereon is thus achieved in this way. However, as the progress in higher resolution displays in recent years has continued, if the memory having a capacity for one screen image is equipped in the liquid crystal driver, it is expected to have a large increase in cost. To solve this problem, low power consumption and low cost are achieved by equipping only memories having a capacity for partial display (partial memory) on the liquid crystal driver.
The area of this partial display may be used in different ways according to specific terminals and applications. Therefore, for example, as disclosed in U.S. Pat. No. 7,123,247 (Japanese Patent Application Laid-Open Publication No. 2003-58130), it is possible to meet various requirements for terminals and applications by equipping a structure where it is capable of arbitrarily setting a partial-display area limited to the physical size of a partial memory.